function foo(a,b){
    console.log(a);//1
    c = 0
    var c;
    a =3
    b=2
    console.log(b);//2
    function b(){}
    console.log(b);//2
}
foo(1)//函数被调用才执行

AO :{
    a:undefined 1 3,
    b:undefined function b(){} 2 ,
    c:undefined
}